1. Field of Invention
The present invention relates to a manufacturing method of a microdisplay. More particularly, the present invention relates to a manufacturing method for improving the non-uniformity of the microdisplay.
2. Description of Related Art
Liquid crystal pixel structure has been widely applied in daily life applications, including liquid crystal televisions, liquid crystal monitors of portable computers or desktop personal computers and liquid crystal projectors. For large-scale displays, the liquid crystal projectors are particularly important. The core element of the liquid crystal projector is the optical engine that generally includes a light source, an optical component consisting of prism pairs and several liquid crystal panels (LCPs) corresponding to different optical paths (R, G, B). The liquid crystal panels, being one type of microdisplays, have pixels of small sizes. Because of the small-sized pixels in the liquid crystal panels, liquid crystal on silicon (LCOS) technology is commonly employed to fabricate the liquid crystal panels.
The LCOS liquid crystal panel is in fact a silicon wafer back panel, by using MOS transistors in place of the thin film transistors used in the conventional liquid crystal displays (LCDs). Since the pixel electrodes of the LCOS liquid crystal panel are made of metal materials, the LCOS liquid crystal panel is a reflective type liquid crystal panel. Moreover, because the metal pixel electrodes completely cover the pixel region, especially the MOS transistors, the LCOS liquid crystal panel is superior in image display compared with conventional LCDs. Hence, the LCOS liquid crystal panels are dominantly used in the liquid crystal projectors.
FIG. 1 is a display view of the structure for the prior art microdisplay under assembly. As shown in FIG. 1, the conventional microdisplay usually includes a silicon wafer substrate 100 with a pixel structure 104 on the front side and a glass plate 102 disposed opposite to the front side of the silicon wafer 100.
FIG. 2 is a cross-sectional view of the prior art microdisplay structure in FIG. 1 after assembly. As shown in FIG. 2, a sealant 106 is usually used to glue the silicon wafer substrate 100 together with the glass plate 102. After cutting the glued glass plate 102 and the silicon wafer substrate 100 into display cells of suitable sizes, liquid crystal is then filled into the space (gap) between the silicon wafer substrate 100 and the glass plate 102.
However, because of the high temperature in the thermal processes and the formation of layers in different materials on the silicon wafer substrate 100, the stress acting on the silicon wafer substrate 100 often leads to distortion or warp in the silicon wafer substrate 100. Once the silicon wafer substrate 100 is distorted, bent or even arched, the central gap 110 of the display cell will be larger than the edge gap 112. Such non-uniformity, resulting from uneven gaps between the silicon wafer substrate 100 and the glass plate 102 in different locations, gives rise to inconsistency in projected images.
Although spacers are implemented in the conventional LCDs to lessen variation of gaps, application of spacers in microdisplays, especially microdisplays of liquid crystal projectors, had better be avoided so as to increase the quality of images.